The invention relates to a drive device for an electric bicycle, particularly for a pedelec driven by electric motor force as well as muscle force.
A drive device for an electric bicycle enables in principle three operating states:                a bicycle operation, where muscle force alone is used as the drive means;        an E-bike operation, where electric motor force alone is used as the drive means; and        a pedelec operation employing muscle force assisted by electric motor force as the drive means, wherein the electric motor does not deliver an output without pedaling, with the exception of a use as a pushing or starting aid up to a speed of 6 km/h. For switching on or controlling the electric motor of a pedelec,                    the force at the pedals, the pedal cranks, the chain, or the wheel, with the use of a signal from a force sensor, and also the torque to be sensed via torque sensors, which torque is transferred by the pedal crankshaft,            the pedaling speed, with the use of the signal from a rotational speed sensor,            the speed of the vehicle, with the use of sensors on the wheel or contactless sensors, or sensors which measure speed independently of the wheels, e.g. by radar or ultrasound, particularly for the purpose of shutting off the electric motor drive starting at a speed of 25 km/h (for pedelecs which are not subject to a license) or 45 km/h (for speed pedelecs);            the accelerationcan be measured and the measurements can be processed further mechanically or electronically in order to switch the electric motor on or off or to control it continuously by means of a control function.                        
The power supplied to the electric motor is calculated by the motor control means based on the sensor data, depending on the selected degree of assistance, so that the electric motor automatically contributes a specified percentage of the power contributed by the rider. The degree of assistance or percentage of power delivered by the electric motor can be adjusted in a plurality of stages, or can be fixed by the manufacturer or a technician.
From EP 2 216 242 A1 is known a drive device with an electric drive for a bicycle driven by muscle force, comprised of a mounting sleeve anchored in a bushing of a frame part of the bicycle, a crankshaft, the ends of which are connected to cranks which are in turn connected to pedals, for muscle force operation, and a cylindrical drive element which is mounted coaxially to the crankshaft, in the mounting sleeve. The cylindrical drive element is comprised of an adapter disk on one end which disk is connected to a drive sprocket. A pedal crank freewheel, serving as a coupling which is dependent on the rotational direction, is disposed between the crankshaft and the cylindrical drive element, and the cylindrical drive element is connected to the rotor of an electric motor via a drive freewheel and a gear unit. Sensors are provided for determining the torque and the rotational speed of the crankshaft, which sensors send signals to an electronic control unit which makes a determination of the power contributed by the rider and controls the electric motor in assisting the rider.
Single-stage or multistage reduction gears are used for transmitting the force from the electric motor to the pedal crankshaft, in particular a single-stage or multistage spur gear or planetary gear, single-stage or multistage chain drives, single-stage harmonic drives, or a combination of these.
From DE 10 2009 045 447 A1 is known a bicycle with an electrical auxiliary drive, comprised of an electric motor, a battery connected to the electric motor for storing electrical energy, a crank assembly with pedal cranks connected to a pedal crankshaft that is disposed so as to be rotatable around a crankshaft axis, and a planetary gear for driving the bicycle with a combination of force from the electric motor and from the muscle force of a rider. The planetary gear and the electric motor which is connected to a sun gear of the planetary gear via a hollow shaft are disposed around the pedal crankshaft of the crank drive, which crankshaft is disposed inside the hollow shaft and is connected either to a planetary gear carrier or to the ring gear of the planetary drive. In order to optimize the torque, the bicycle has a gear shift formed as a derailleur or a hub gear connected to the planetary gear.
A drawback connected with the use of a single-stage or multistage spur gears or chain gears is the large amount of installation space needed to accommodate these types of drives, the increased material use required thereby for the drive housing components, and the substantial amount of space needed for connecting the drive device to the bicycle frame. When the drive device is mounted in the area of the pedal crankshaft, this leads to projecting parts of the drive housing which pose hindrances in transporting the bicycle. A further drawback connected with the use of gear drives or chain drives is the inconvenient amount of noise emitted, and in the case of gear drives, as a result of the rigid connection of the electric motor with the pedal crankshaft, high vulnerability to shocks, caused, e.g., by switching surges of the derailleur or the hub gear of the bicycle.
Chain stages of a single-stage or multistage chain drive disposed outside the drive housing are susceptible to external influences, and they increase the risk of injury. The use of a single-stage harmonic drive gear leads to increased costs and a reduction of the efficiency.
EP 0 763 462 B1 discloses an auxiliary drive for a bicycle, which is comprised of a frame with a bottom bracket, a seat tube, a lower tube, a head tube, an upper tube, a pair of chain bars, and a pair of seat bars. The lower tube, seat tube, and chain bars intersect at a bottom bracket with a crankshaft, the ends of which are connected to crank arms. The auxiliary drive comprises an electric motor, a power transmission belt, and a gear train comprised of a plurality of spur gears, which gear train is coupled on its end side to the crankshaft. The auxiliary drive is disposed in a housing having a flat, elongated shape, with two semicircular ends, which housing is comprised of an inner and an outer housing, both of which have an elongated pan-shaped configuration. The inner housing extends forward from the bottom bracket of the bicycle frame along the lower tube, and is open on a side opposite to the lower tube. The outer housing is also open, on the side opposite to the opening of the inner housing, and has a recess into which the open end of the inner housing fits. The inner and outer housing are interconnected by a combination of a plurality of screws.
As a result of the reducing drive comprised of a gear train with a plurality of intermeshing spur gears, and the associated elongated plate-shaped housing components, the housing extends far below the lower tube, from the bottom bracket, which causes a substantial reduction in the ground clearance in the area of the bottom bracket, and consequently, when the bicycle is transported over irregularities in the ground, there is an increased risk of collision with obstacles such as stairs, curbs, and the like.